Semiconductor device having SOI structure and method for manufacturing the same

ABSTRACT

In a semiconductor device, a gate electrode, an impurity diffused region, a body potential fixing region, a first insulator, and a dummy gate electrode are provided on top of an SOI substrate consisting of an underlying silicon substrate, a buried insulator, and a semiconductor layer. The impurity diffused region is a region formed by implanting an impurity of a first conductivity type into the semiconductor layer around the gate electrode. The body potential fixing region is a region provided in the direction of an extension line of the length of the gate electrode and implanted with an impurity of a second conductivity type. The first insulator is formed at least in the portion between the body potential fixing region and the gate electrode. The dummy gate electrode is provided on the first insulator between the body potential fixing region and the gate electrode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and a method formanufacturing a semiconductor device and, in particular, to asemiconductor device having an SOI structure and a method formanufacturing the same.

2. Background Art

The SOI (Silicon On Insulator) substrate of transistors having an SOIstructure consists of a multilayered stack of an underlying siliconsubstrate, a buried insulator, and an SOI layer. A gate electrode isformed on top of a gate insulator on the SOI substrate. The SOI layer isseparated into active areas by a partial isolation insulator. Thepartial isolation insulator is formed by filling a trench in the SOIlayer with an insulator such as an oxide. The trench is formed down to adepth such that it does not completely penetrate through the SOI layer.The portion of SOI layer left under the partial isolation insulator actsas a well.

A portion of the SOI layer under the gate electrode is a channel region.Impurity diffused layers (extension and source/drain) are formed on bothsides of the channel region. A body potential fixing region for fixing abody potential is provided on the opposite side of the partial isolationinsulator from the channel region. The channel region and the bodypotential fixing regions are electrically interconnected through thewell.

For forming the body potential fixing region and the impurity diffusedregions on both sides of the gate electrode, ions of opposite types areimplanted respectively. During the ion implantation of the source/drain,therefore, the body potential fixing region is masked with a resist;during the ion implantation of the body potential fixing region, theimpurity diffused layer is masked with a resist.

The gate electrode is separated from the body potential fixing region bythe partial isolation insulator. When ion implantation is performed,typically a resist mask is not provided on the partial isolationinsulator. During such ion implantation, ions are also implanted intothe partial isolation insulator.

In SOI semiconductor devices, the partial isolation insulator is verythin. Accordingly, when ions are implanted into the partial isolationinsulator without a mask, some of the ions may penetrate through thepartial isolation insulator into the well under it. If ions areimplanted into the well, the resistance of the well, from the bodypotential fixing region to the channel region, may increase and thusisolation characteristics can degrade.

To prevent this problem, an approach has been proposed in which a resistmask used during source/drain implantation is provided so as to coverthe partial isolation insulator between the gate electrode and the bodypotential fixing region as well as the body potential fixing region, andthe ion implantation is performed with the resist mask to preventundesired impurity from penetrating into the well (for example seeJapanese Patent Laid-Open No. 2002-208705).

Especially during ion implantation of the impurity diffused layers(extension and source/drain), ions must be precisely implanted in properpositions on both sides of the gate electrode. Therefore, when a resistmask is provided on the partial isolation insulator as stated above, theresist mask must be precisely aligned with the gate electrode. However,precise alignment of the resist is difficult to achieve. If the resistmask cannot precisely be formed and unnecessarily overlaps the gateelectrode, sufficient ions cannot be implanted in proper positions.

SUMMARY OF THE INVENTION

Therefore, the present invention provides an improved semiconductordevice and a method for manufacturing the same which enable ionimplantation for forming an impurity diffused layer while preventingions from penetrating through a partial isolation insulator even if itis thin.

According to one aspect of the present invention, a semiconductor devicecomprises a substrate including an underlying silicon substrate, aburied insulator, and a semiconductor layer. A first gate electrode isformed on a gate insulator on the semiconductor layer. A first impuritydiffused region is formed in a region around the first gate electrode inthe direction of the length of the first gate electrode in thesemiconductor layer by implanting with an impurity of a firstconductivity type. A second impurity diffused region is formed in aregion in the semiconductor layer in the direction of an extension lineof the length of the first gate electrode by implanting with an impurityof a second conductivity type opposite the first conductivity type. Afirst insulator is formed at least on a region of the semiconductorlayer between the second impurity diffused region and the first gateelectrode. A second gate electrode formed on the first insulator betweenthe second impurity diffused region and the first gate electrode.

According to another aspect of the present invention, in a method formanufacturing a semiconductor device, a first insulator is formed so asto separate a semiconductor layer of a silicon-on-insulator substrateincluding an underlying substrate, a buried insulator formed on top ofthe underlying substrate and a semiconductor layer formed on top of theburied insulator, into a first and a second regions. A gate insulator isformed on the semiconductor layer. A first gate electrode is formed onthe first region and a second gate electrode is formed on the firstinsulator. A first resist mask is formed so as to cover the secondregion. An impurity of a first conductivity type is implanted into thefirst region by using the first resist mask and the first and secondgate electrodes as a mask and then, the first resist mask is removed. Asecond resist mask is formed so as to cover the first region. A secondimpurity of a second conductivity type is implanted into thesemiconductor layer by using the second resist mask and then, the secondresist mask is removed

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic cross-sectional views illustrating asemiconductor device according to a first embodiment of the presentinvention;

FIG. 2 is a flowchart illustrating a method for manufacturing asemiconductor device according to the first embodiment of the presentinvention;

FIGS. 3A to 11B are schematic diagrams illustrating states in a processof manufacturing the semiconductor device according to the firstembodiment of the present invention;

FIGS. 12A and 12B are schematic diagrams illustrating another exemplarysemiconductor device according to the first embodiment of the presentinvention;

FIGS. 13A to 13C are schematic diagrams illustrating a semiconductordevice according to a second embodiment of the present invention;

FIGS. 14A to 14C are schematic diagrams illustrating a process formanufacturing the semiconductor device according to the secondembodiment of the present invention;

FIGS. 15A to 15C are schematic diagrams illustrating another exemplarysemiconductor device according to the second embodiment;

FIGS. 16A and 16B are schematic diagrams illustrating a semiconductordevice according to a third embodiment of the present invention;

FIG. 17 is a flowchart illustrating a method for manufacturing thesemiconductor device according to the third embodiment of the presentinvention;

FIGS. 18A and 18B are schematic cross-sectional views illustratingprocess steps for manufacturing the semiconductor device according tothe third embodiment of the present invention;

FIGS. 19A and 19B are schematic diagram illustrating a semiconductordevice according to a fourth embodiment of the present invention;

FIG. 20 is a schematic diagram illustrating another exemplarysemiconductor device according to the fourth embodiment of the presentinvention;

FIG. 21 is a schematic diagram illustrating another exemplarysemiconductor device according to the fourth embodiment of the presentinvention;

FIGS. 22A to 24B are schematic diagrams illustrating process steps formanufacturing a semiconductor device according to a fifth embodiment ofthe present invention;

FIG. 25 is a top view illustrating a semiconductor device according to asixth embodiment of the present invention;

FIGS. 26 and 27 are cross-sectional views of the semiconductor deviceaccording to a sixth embodiment of the present invention;

FIGS. 28A and 28B are schematic diagrams illustrating a semiconductordevice according to a seventh embodiment of the present invention;

FIG. 29 is a flowchart illustrating a method for manufacturing asemiconductor device according to the seventh embodiment of the presentinvention;

FIGS. 30 to 38 are schematic cross-sectional view illustrating processsteps for manufacturing the semiconductor device according to theseventh embodiment of present invention;

FIG. 39 is schematic cross-sectional view illustrating process step formanufacturing another exemplary semiconductor device according to theseventh embodiment of the present invention;

FIGS. 40A and 40B are schematic diagram illustrating a semiconductordevice according to an eight embodiment of the present invention;

FIG. 41 is a schematic diagram illustrating a semiconductor deviceaccording to a ninth embodiment of the present invention;

FIGS. 42 to 44 are schematic diagrams illustrating process steps formanufacturing the semiconductor device according to the ninth embodimentof the present invention;

FIGS. 45 to 47 are schematic diagrams illustrating a semiconductordevice according to a tenth embodiment of the present invention;

FIGS. 48A to 51B are schematic diagrams illustrating process steps formanufacturing another exemplary semiconductor device according to atenth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be descried with reference tothe accompanying drawings. Through the drawings, like or equivalentelements are labeled like reference numerals and the description thereofwill be simplified or omitted.

While specific numerical quantities such as numbers, quantities,amounts, and ranges of elements are referred to in the followingdescription of embodiments, the present invention is not limited to thespecific numerical quantities unless otherwise stated or unless clearlyapparent from principle. Also, structures and steps of methods describedwith respect to the embodiments are not essential to the presentinvention unless otherwise stated or clearly apparent from principle.

Part “A” of each of FIGS. 1 to 23, excluding FIG. 2, illustrates a topview, in which spacers and sidewalls on the sides of electrode are notdepicted for simplicity unless specifically described. Also, in thefollowing description, the vertical direction in part “A” of each figurewill be referred to as the Y-direction and the horizontal direction willbe referred to as the X-direction for convenience.

First Embodiment

FIGS. 1A and 1B are schematic cross-sectional views illustrating asemiconductor device according to a first embodiment of the presentinvention. FIG. 1A is a top view of the semiconductor device and FIG. 1Billustrates a cross-sectional view taken on line Y-Y′ of FIG. 1A.

As shown in FIGS. 1A and 1B, the substrate of the semiconductor deviceis an SOI (Silicon on Insulation) substrate having a multilayeredstructure including an underlying silicon substrate 2, a buriedinsulator 4 (buried insulator film), and an SOI layer 6 (semiconductorlayer). The term “SOI layer” as used herein refers to the topsemiconductor layer of the SOI substrate.

A partial isolation insulator 8 (first isolator) is formed in the SOIlayer 6 and separates the SOI layer into active areas. The partialisolation insulator 8 is formed down to a depth such that a certainthickness of the SOI layer 6 is left under it.

A gate electrode 14 (first gate electrode) is formed on a gate insulator12 on the SOI layer 6. However, the ends 14 a, 14 b of the longitudinaldirection (i.e. in the Y-direction) of the gate electrode 14 are formedon the partial isolation insulator 8, where the gate insulator film 12is not formed between the gate electrode 14 and the SOI layer 6. A dummygate electrode 16 (second gate electrode) is formed at a position on anextension line in the longitudinal direction (i.e. in the Y-direction)of the gate electrode 14 on the partial isolation insulator 8, that is,at a position opposed to end 14 b of the gate electrode. The term “dummygate electrode” as used hereinafter refers to an electrode that is notconnected to an actual wiring or, if connected, does not function as agate electrode in the semiconductor device.

In the Y-Y′ cross-section shown in FIG. 1B, the portion of the SOI layer6 under the partial isolation insulator 8 is a well 18. The well 18 is ap-well, for example, if the adjacent transistor shown is an nMOStransistor. impurity diffused layers (extension and source/drain) 20(first impurity diffused region) are formed on both sides of the gateelectrode 14 of the surface of the SOI layer 6. The impurity diffusedlayers 20 are regions doped with an n-type impurity, for example, if thetransistor is an nMOS transistor. A body potential fixing region 22(second impurity diffused region) is formed on the opposite side on theSOI layer 6 of the partial isolation insulator 8 from the gate electrode14. The body potential fixing region 22 is a region doped with animpurity of the type opposite that of the impurity diffused layers 20(that is, the same type as that of the channel region under the gateelectrode 14). For example, if the transistor is an nMOS transistor, thebody potential fixing region 22 is an area doped with a p-type impurity.This means that the channel region in the SOI layer 6 under the gateelectrode 14 is electrically connected with the body potential fixingregion 22 through the well 18. The potential of the body potentialfixing region 22 can be fixed from an external source.

Formed on the sides of the gate electrode 14 and the dummy gateelectrode 16 are spacers 24 made of a silicon oxide. Formed on the sideof each spacer 24 is a silicon oxide film 26 and a silicon nitride film28 as a sidewall. The distance between the dummy gate electrode 16 andthe body potential fixing region 22 is equal to the combined width ofthe spacer 24 and the sidewall (26, 28). In other words, the spacebetween the dummy gate electrode 16 and the body potential fixing region22 is filled with the spacer 24 and the sidewall (26, 28).

In the semiconductor device 100 configured as described above, thepotential of the SOI substrate of the transistor can be fixed from anexternal source through an external connection line connected to thebody potential fixing region 22 through a body contact (not shown), byway of the body potential fixing region 22 and the well 18.

The dummy gate electrode 16 is formed on the partial isolation insulator8 between end 14 a of the gate electrode 14 and the body potentialfixing region 22 in the semiconductor device 100. The dummy gateelectrode 16 functions as a mask for the partial isolation insulator 8during ion implantation for forming the impurity diffused layers 20.Accordingly, the amount of ions implanted into the partial isolationinsulator 8 is minimized and therefore the amount of ions penetratinginto the well 18 through the partial isolation insulator 8 is alsominimized.

FIG. 2 is a flowchart illustrating a method for manufacturing asemiconductor device 100 according to the first embodiment of thepresent invention. FIGS. 3A to 11B are schematic diagrams illustratingstates in a process of manufacturing the semiconductor device 100. Part“A” of each of FIGS. 3 to 11 shows a top view corresponding to the onein FIG. 1A and part “B” depicts a cross-section corresponding to the onein FIG. 1B(b).

While the method according to the first embodiment is also applied whena CMOS or pMOS is formed, the following description will focus on a casewhere an nMOS transistor is formed and the figures mainly depict thenMOS transistor, for simplicity.

First, a silicon oxide film 30 and a silicon nitride film 32 are formedon an SOI substrate consisting of a underlying silicon substrate 2, aburied insulator 4, and an SOI layer 6 which has a thickness of 30 to200 nm or so (steps S2 and S4). Then, a resist pattern 34 for forming atrench is formed by photolithography as shown in FIGS. 3A and 3B (stepS6). The resist pattern 34 has an opening over a portion where thepartial isolation insulator 8 will be formed.

Then, the silicon nitride film 32 and the silicon oxide film 30 areetched by using the resist pattern 34 as a mask to form a trench with apredetermined depth in the SOI layer 6 (step S8). The trench is formedin such a manner that a certain thickness of the SOI layer 6 is leftunder the trench. Then, the resist pattern 34 is removed (step S10) andthermal oxidization is performed (step S12). As a result, a siliconoxide film 8 a is formed on the inner wall of the trench in the portionwhere the SOI layer 6 is exposed, as shown in FIGS. 4A and 4B. Then, atleast the trench is filled with a silicon oxide film 8 b as shown inFIGS. 5A and 5B (step S14) and annealing is performed (step S16).

It should be noted that the trench is directly filled with the siliconoxide film without forming the silicon oxide film 8 a by thermaloxidation. Annealing is not necessary after the filling with the siliconoxide film 8 b.

Then, a resist film is applied to the entire surface to form a resistpattern for etching and then etching is performed (step S18), and thesurface is then planarized by CMP (Chemical Mechanical Polishing) (stepS20). Then, the silicon nitride film 32 left on the surface is removed(step S22). As a result, the trench is filled with the silicon oxidefilms 8 a and 8 b to form a partial isolation insulator 8 as shown inFIGS. 6A and 6B.

Then, a gate insulator film 12 is formed by thermal oxidation (step S24)and a polysilicon film for providing a gate electrode 14 and a dummygate electrode 16 is formed (step S26).

The polysilicon film is then patterned (step S28) in such a manner thatminimum distance of the design rule between the gate electrode 14 andthe dummy gate electrode 16 is provided and that the distance betweenthe body potential fixing region 22 and the dummy gate electrode 16becomes equal to the combined width of a spacer 24 and sidewall.

More specifically, in the patterning of the polysilicon film, a resistpattern is first formed by photolithography and then the polysiliconfilm is etched by using the resist pattern as a mask. As a result, thegate electrode 14 and the dummy gate electrode 16 with desired shapesare formed as shown in FIGS. 7A and 7B.

Then, spacers 24 are formed on the sides of the gate electrode 14 andthe dummy gate electrode 16 as shown in FIGS. 8A and 8B (step S30). Thespacers 24 may be formed by for example evenly depositing an oxide filmon the gate electrode 14 and the dummy gate electrode 16 and thenperforming anisotropic etching.

Then ion implantation for forming an extension in impurity diffusedlayers 20 is performed (step S32). Before ion implantation for formingthe extension, a resist mask 36 is formed first so that it covers thebody potential fixing region 22, and then ion implantation for formingthe extension is performed. In particular, if an nMOS is to be formed,n-type ions are implanted. The resist mask 36, the gate electrode 14,the dummy gate electrode 16 function as a mask during the ionimplantation. Thus, n-type ions are implanted into the SOI layer 6 onboth sides of the gate electrode 14 to form an extension. The gateelectrode 14 is prevented from being damaged by the ion implantationbecause the sides of the gate electrode 14 are protected by the spacers24.

Also, the dummy gate electrode 16 formed on the partial isolationinsulator 8 acts as a mask during the ion implantation. Accordingly, theamount of ions implanted into the partial isolation insulator 8 abovethe well 18 can be minimized and therefore the amount of ionspenetrating into the well 18 can be minimized. Furthermore, ions do notpenetrate into the body potential fixing region 22 because it is coveredwith the resist mask 36.

Then, p-type ions are implanted to form a pocket (not shown) surroundingthe bottom of the extension. As with the case of the extensionimplantation, the gate electrode 14, the dummy gate electrode 16, andthe resist mast 36 function as a mask during in this implantation. Theresist mask 36 is removed after the ion implantation for forming thepocket.

Then, ions are implanted into the body potential fixing region 22 (stepS34). Before the ion implantation, a resist mask 38 is formed to coverthe area where the nMOS transistor is to be formed, as shown in FIGS. 9Aand 9B. Then, p-type ions are implanted into the body potential fixingregion 22 using the resist mask 38 as a mask. If a pMOS transistor is tobe formed in a location not shown, an extension similar to that of thenMOS is formed on both sides of the gate electrode of the pMOStransistor. In that case, n-type ions are implanted, as required, toform a pocket surrounding the extension. The resist mask 38 is thenremoved.

Then, sidewalls are formed as shown in FIGS. 10A and 10B (step S36). Inparticular, first a silicon oxide film 26 and a silicon nitride film 28are deposited in this order. Then, etch-back is performed so that thesilicon oxide film 26 and the silicon nitride film 28 are left only onthe sides of the gate electrode 14 and the dummy gate electrode 16. As aresult, sidewalls are formed. The etch-back is performed in such amanner that the thickest portion of the combination of the spacer 24 andthe sidewall (26, 28) (namely the width of the bottom portion of thesidewall in FIG. 10B) becomes equal to the distance between the bodypotential fixing region 22 and the dummy gate electrode 16. In otherwords, the etch-back is performed so that the surface between the dummygate electrode 16 and the body potential fixing region 22 is filled withthe spacers 24 and the sidewalls (26, 28).

Then, ion implantation for forming the source/drain in the impuritydiffused layers 20 of the nMOS transistor is performed (step S38). Aswith the formation of the extension, a resist mask 40 that covers thebody potential fixing region 22 is formed as shown in FIGS. 11A and 11B.The space between the body potential fixing region 22 and the dummy gateelectrode 16 is filled with the spacer 24 and the sidewall (26, 28).This means that the spacer 24 and the sidewall (26, 28) functions as amask for the space between the dummy gate electrode 16 and the bodypotential fixing region 22 during ion implantation. Accordingly, thealignment of the resist mask 40 does not need to be highly precise; theresist mask 40 maybe formed to cover at least the body potential fixingregion 22.

N-type ion implantation is performed using the resist mask 40, the gateelectrode 14, the dummy gate electrode 16, and their spacers 24 andsidewalls 26, 28 on the side as a mask. As a result, implantation of thesource/drain having a deep junction and a relatively high impurityconcentration is completed in the SOI layer 6 on the both sides of thegate electrode 14 and a impurity diffused layers 20 are formed in theSOI layer 6 around the gate electrode 14. The ions are implanted withhigh energy and concentration. However, the amount of ions implantedthrough the partial isolation insulator 8 into the well 18 under it issufficiently small because the partial isolation insulator 8 is coveredto some extent by the dummy gate electrode 16. The resist mask 40 isremoved after the ion implantation.

Then, ions are implanted into the body potential fixing region 22 (stepS40). As with the ion implantation in the nMOS transistor at step S34, aresist mask is first formed that covers regions into which p-type ionsare not to be implanted. Then p-type ions are implanted by using theresist mask and the dummy gate electrode 16 and the spacer 24 andsidewall 26, 28 formed on the sides of the dummy gate electrode 16 as amask. With this, p-type ions are heavily implanted into the bodypotential fixing region 22, completing the body potential fixing region22. At the same time, the source/drain of the pMOS transistor, notshown, are formed. Then, the resist mask is removed. Thermal treatingfor activation is performed as needed.

After the process described above, an insulator film is formed to coverthe elements such as the gate electrodes formed on the substrate andthen planarized by CMP. In particular, an insulator film is formed withthe dummy gate electrode 16 left formed on the substrate, in addition tothe gate electrode 14, to cover them and then CMP is performed. Thus,planarization can be performed on a uniformly flat surface of theinsulator.

Then, contact plugs connecting to the impurity diffused layers 20 andthe body potential fixing regions 22 are formed. By forming a requiredlayer such as a multilevel interconnection layer is further formed onthe insulator film to complete the semiconductor device.

As has been described, according to the first embodiment, the dummy gateelectrode 16 formed on the partial isolation insulator 8 functions as amask during the ion implantation for forming the impurity diffusedlayers 20. This can inhibit ions from penetrating into the partialisolation insulator 8 and consequently inhibit penetrating through thepartial isolation insulator 8 into the well 18 under it. Therefore,degradation of isolation characteristics of the well 18 connecting thechannel region and the body potential fixing region 22 can be inhibitedto provide a semiconductor device with good device characteristics.

Specifically, consider the resistance between the channel region and thebody potential fixing region 22. For example, if the resistance of thesemiconductor layer under end 14 b of the gate electrode is 100Ω/sheetfor each of the 2 sheets, that is, 200Ω in total, and the resistance ofthe well 18 under the partial isolation insulator 8 is 1,000Ω/sheet,that is, 1,000Ω in total, in a semiconductor device in which a dummygate electrode 16 is not formed, then the resistance of the wholesemiconductor device will be 1,200Ω. It is important to note that thesheet resistance of the well 18 under the partial isolation insulator 8is high because ions have penetrated into the well 18.

In contrast, in the semiconductor device having a similar structure butwith a dummy gate electrode 16 formed thereon so as to cover the partialisolation insulator 8, the sheet resistance of the portion covered withthe dummy gate electrode 16 is the same as the sheet resistance of theSOI layer 6 under the end 14 b of the gate electrode, that is,100Ω/sheet. The sheet resistance of a region of the partial isolationinsulator 8 on which the dummy gate electrode 16 is not formed maybe,for example, 1,000Ω/sheet because ions have been penetrated in thisportion. However, the area of this portion is smaller than that in theconventional semiconductor device, for example 0.5 sheet. Thus, theresistance of the portion under the end 14 b of the gate electrode is200Ω, the resistance of the portion under the partial isolationinsulator 8 in which ion has been penetrated is 500Ω, the resistance ofthe portion under the partial isolation insulator 8 on which the dummygate electrode 16 is formed is approximately 100Ω. Therefore, theresistance of the whole semiconductor device is approximately 800Ω.

Thus, the resistance between the body potential fixing region 22 and thechannel region can be minimized by forming the dummy gate electrode 16.

FIGS. 12A and 12B are a schematic diagrams illustrating anotherexemplary semiconductor device according to the first embodiment of thepresent invention. FIG. 12A illustrates a top view of the semiconductordevice and FIG. 12B illustrates a cross-section taken on line Y-Y′ ofFIG. 12A.

The semiconductor device shown in FIGS. 12A and 12B is the same as thesemiconductor device 100 shown in FIGS. 1A and 1B, except that a dummygate electrode 116 overlaps a portion of the body potential fixingregion 22.

In the semiconductor device shown in FIGS. 12A and 12B, the SOI layer 6is not exposed in the space between the body potential fixing region 22and the dummy gate electrode 116. This arrangement eliminates the needfor an precise alignment of a resist mask with the dummy gate electrode116 when the resist mask covering the body potential fixing region 22 isformed before implantation of impurity diffused layers (extension andsource/drain) 20 of the transistor. Furthermore, in the event of amisalignment of the resist mask formed, the dummy gate electrode 116 caneffectively inhibit penetration of an undesirable impurity (that is, animpurity of the opposite type) into the body potential fixing region 22.Consequently, degradation of isolation characteristics between the bodypotential fixing region 22 and the well 18 can be prevented to provide asemiconductor device with good device characteristics.

While the first embodiment has been described and depicted, forconvenience, with respect to an nMOS transistor and a p-typebody-potential-fixing region 22 which fixes the potential of the nMOStransistor, the present invention can be applied to devices such as CMOSdevices. Therefore, a pMOS transistor and an n-typebody-potential-fixing region can be formed in other regions at the sametime in a similar manner.

Second Embodiment

FIGS. 13A to 13C are schematic diagrams illustrating a semiconductordevice 200 according to a second embodiment of the present invention.FIG. 13A illustrates a top view of the semiconductor device 200, FIG.13B is a cross-sectional view taken on line Y-Y′ of FIG. 13A, and FIG.13C is across-sectional view taken on line X-X′ of FIG. 13A. FIGS. 14Ato 14C are schematic diagrams illustrating a process for manufacturingthe semiconductor device 200 according to the second embodiment of thepresent invention. FIGS. 14A to 14C illustrate portions corresponding tothose shown in FIGS. 13A to 13C, respectively.

The semiconductor device 200 according to the second embodiment has thesame structure as that of the semiconductor device 100 shown in FIGS. 1Aand 1B, except that the semiconductor device 200 has a completeisolation insulator (complete isolation region) 42. In particular, thesemiconductor device 200, like the semiconductor device 100, has a dummygate electrode 16 on an partial isolation insulator 8 to inhibit ionsfrom penetrating through the partial isolation insulator 8 into anunderlying well 18.

The complete isolation insulator 42 of the semiconductor device 200 isprovided on both sides of end 14 b of a gate electrode 14, that is, thegate electrode end 14 b on the body-potential-fixing-region 22 side. Thecomplete isolation insulator 42 is formed by etching the SOI layer 6 onboth sides of the 14 b of the gate electrode 14 down to a buriedinsulator 4 and filling the etched portion with a silicon oxide film, asshown in FIG. 13C.

The provision of the complete isolation insulator 42 at end 14 b of thegate electrode 14 can reduce the parasitic capacitance.

The method for manufacturing the semiconductor device 200 is similar tothe method for manufacturing the semiconductor device 100, except that agroove for forming the complete isolation insulator 42 is formed after atrench for forming an partial isolation insulator 8 is formed (steps S6to S10). In particular, as shown in FIGS. 14A to 14C, a resist mask 44having an opening at the region where the complete isolation insulator42 is to be provided is formed, then the region of the SOI layer 6 wherethe complete isolation insulator 42 is to be formed is etched down tothe buried insulator 4 by using the resist mask 44 as a mask. Then, thetrench and groove formed in the SOI layer 6 are filled with a siliconoxide film and planarized, as in steps S12 to S22 of the firstembodiment, thus forming the partial isolation insulator 8 and thecomplete isolation insulator 42 at a time.

The remainder of the manufacturing method is performed in a similar wayas in steps S24 to S40 described with respect to the first embodiment.Thus, the semiconductor device 200 can be completed.

As has been described above, a complete isolation insulator 42 is formedon both sides of one end of the gate electrode in the second embodiment.This completely isolates both sides of the end 14 b of the gateelectrode 14 from each other. Accordingly, the resistance between thechannel region under the gate electrode 14 and the body potential fixingregion 22 can be minimized and therefore the body potential can be fixedmore stably.

Furthermore, the semiconductor device can be manufactured with a minimumnumber of additional steps because the complete isolation insulator 42and the partial isolation insulator 8 can be formed at a time.

While the second embodiment has been described with respect to a casewhere the complete isolation insulator 42 is formed on both sides of theend 14 b of the gate electrode 14, the present invention is not solimited. For example, the complete isolation insulator can be formed onboth sides of the other end 14 a of the gate electrode 14 in a similarmanner. This can also reduce the resistance of the transistor.Furthermore, formation of a complete isolation insulator is not limitedto selective formation described above. For example, a completeisolation insulator may be formed by removing all of the SOI layer 6except the portions where the SOI layer 6 must be left, such as active aregion where a transistor is to be formed, a region where a bodypotential fixing region 22 is to be formed, and a region where a well 18interconnecting the channel region under the gate and the body potentialfixing region 22 is to be formed. This can further reduce the resistanceof the transistor.

FIGS. 15A to 15C are schematic diagrams illustrating another exemplarysemiconductor device according to the second embodiment. FIG. 15A is atop view and FIGS. 15B and 15C illustrate cross-sections taken on lineY-Y′ and line X-X′, respectively, of FIG. 15A.

The semiconductor device 210 shown in FIGS. 15A to 15C is the same asthe semiconductor device 200 in FIGS. 13A to 13C, except that the gateelectrode 14 is replaced with a gate electrode 114 having a shape asshown in FIGS. 15A to 15C. In particular, end 114 b of the gateelectrode 114 is horizontally (in the X-direction) widened when viewedfrom above. The overlap between end 114 b of the gate electrode 114 andthe complete isolation insulator 42 is large because of the widened end114 b of the gate electrode 114. By widening end 114 b of the gateelectrode 114 to enlarge the overlap with the complete isolationinsulator 42 in this way, the margin for alignment between the completeisolation insulator 42 and gate electrode 114 during exposure of thecomplete isolation insulator 42 and gate electrode 114 can be increased.Furthermore, if a misalignment occurs, the 114 b of the gate electrode114 and the complete isolation insulator 42 can be overlapped withoutfail. Thus, the parasitic capacitance can be further reduced by anamount equivalent to the overlap of the end 114 b of the gate electrode114 and the complete isolation insulator 42.

Third Embodiment

FIGS. 16A and 16B are schematic diagrams illustrating a semiconductordevice 300 according to a third embodiment of the present invention.FIG. 16A illustrates a top view of the semiconductor device 300 and FIG.16B illustrates a cross-section taken on line Y-Y′ of FIG. 16A.

The semiconductor device 300 according to the third embodiment shown inFIGS. 16A and 16B is the same as the semiconductor device 100 in FIGS.1A and 1B, except that the space between a gate electrode 14 and a dummygate electrode 16 is filled with a silicon oxide film 50 (secondisolator).

FIG. 17 is a flowchart illustrating a method for manufacturing thesemiconductor device 300 according to the third embodiment. FIGS. 18Aand 18B are schematic cross-sectional views illustrating process stepsfor manufacturing the semiconductor device 300. FIGS. 18A and 18Billustrate portions corresponding to those in FIGS. 16A 16B,respectively.

The manufacturing process shown in the flowchart of FIG. 17 is performedbetween steps S34 and S38 of the manufacturing process shown in theflowchart of FIG. 2. That is, after steps similar to steps S2 to S34 areperformed, sidewalls (26, 28) are formed (step S302) in a manner similarto that at step S36.

Then, the space between the gate electrode 14 and the dummy gateelectrode 16 is filled with a silicon oxide film 50 (step S304) as inFIGS. 18A and 18B. In particular, a silicon oxide film 50 is firstformed on the entire surface of the substrate on which all elements upto the sidewalls (26, 28) are formed. The thickness T₅₀ of the siliconoxide film 50 to be formed is such that the following Equation (1) issatisfied:T ₅₀≧(Y−2X)/2  (1)Here, X represents the width of the widest portion the sidewall (26, 28)and a spacer 24 and Y represents the distance between a gate electrode14 and a dummy gate electrode 16 (or the distance between dummy gateelectrodes 16).

Then, etch-back is performed using anisotropic etching (step S306).During this etch-back, the silicon oxide film 50 having the shape of aspacer is formed on the sides of the gate electrode 14 or the dummy gateelectrode 16 in a portion where the distance to a nearby elements islarge. On the other hand, the silicon oxide film 50 is buried in aportion where the distance to a nearby elements is small, such as theportion where the gate electrode 14 opposes the dummy gate electrode 16.In this way, the space between the gate electrode 14 and the dummy gateelectrode 16 is filled with the silicon oxide film 50.

Then, the silicon oxide film 50 having the shape of a spacer left on thesides of the gate electrode 14 or dummy gate electrode 16 in the portionwhere the distances to the nearby elements are large is removed (stepS308). Thus, the silicon oxide film 50 filling the space between thedummy gate electrode 16 and the gate electrode 14 is formed.

As with the first embodiment, ion implantation is performed for formingthe source/drain in the impurity diffused layers 20 at step S38 in FIG.2. Because the space between the dummy gate electrode 16 and the gateelectrode 14 is filled with the silicon oxide film 50, ions areinhibited from penetrating into the partial isolation insulator 8through the space between the dummy gate electrode 16 and the gateelectrode 14 during the ion implantation.

Thus, the semiconductor device 300 shown in FIGS. 16A and 16B isprovided.

As has been described above, according to the third embodiment, thesilicon oxide film 50 is formed to fill the space between the gateelectrode 14 and the dummy gate electrode 16 after the sidewalls (26,28) are formed. Therefore, ions can be more reliably prevented frompenetrating into the partial isolation insulator 8 during source/drainimplantation. Accordingly, also in the portion of the SOI layer 6between the gate electrode 14 and the dummy gate electrode 16, ions canbe inhibited from penetrating through the partial isolation insulator 8,thereby preventing degradation of isolation characteristics of thesemiconductor device further reliably.

While the third embodiment has been described with a case where thespace between the gate electrode 14 and the dummy gate electrode 16 inthe semiconductor device 100 in the first embodiment 1 is filled with asilicon oxide film 50, the present invention is not so limited. Forexample, the third embodiment can be combined with any of the othersemiconductor devices described in the first and second embodiments. Forexample, it can be combined with the structure in which the bodypotential fixing region 22 and the dummy gate electrode 16 partiallyoverlap as described with respect to a variation of the first embodiment(FIGS. 12A and 12B), the structure in which a complete isolationinsulator 42 is provided as in the semiconductor device 200 described inthe second embodiment (FIGS. 13A to 13C), or a structure in which oneend 114 b of the gate electrode 114 is wide (FIGS. 15A to 15C).

While the third embodiment has been described with a case where thesilicon oxide film 50 is formed such that it has the thickness as givenby Equation (1), the present invention is not so limited. The siliconoxide film 50 may have any thickness that can reliably fill the spacebetween the dummy gate electrode 16 and the gate electrode 14.

Fourth Embodiment

FIGS. 19A and 19B are schematic diagram illustrating a semiconductordevice 400 according to a fourth embodiment of the present invention.FIG. 19A illustrates a top view of the semiconductor device and FIG. 19Billustrates a cross-section taken on line Y-Y′ of FIG. 19A.

The semiconductor device 400 according to the fourth embodiment is thesame as the one shown in FIGS. 1A and 1B, except that a dummy gateelectrode 52 surrounding impurity diffused layers 20 is formed as shownin FIGS. 19A and 19B. As with the sides of the dummy electrode 16,formed on the side of the dummy gate electrode 52 is a spacer 24 made ofa silicon oxide film, and a sidewall made of a silicon oxide film 26 anda silicon nitride film 28. The combined thickness of the spacer 24 andthe sidewall (26, 28) is equal to the distance between the dummy gateelectrode 52 and the impurity diffused layers 20. In other words, thespace between the dummy gate electrode 52 and the impurity diffusedlayers 20 is filled with the spacer 24 and the sidewall (26, 28).

The semiconductor device 400 can be manufactured using a method similarto the method for manufacturing the semiconductor device 100. However,for patterning (step S28) after polysilicon for forming a gate electrode14 is deposited, a resist mask is also formed on a portion where dummygate electrode 52 is to be formed, and is used as a mask in etching.Thus, the dummy gate electrode 52 can be formed together with the gateelectrode 14 and the dummy gate electrode 16 at a time. The spacer 24and the sidewall on the side of the dummy gate electrode 52 can beformed together with the spacers 24 and sidewalls (26, 28) of the gateelectrode 14 and dummy gate electrode 16 at a time. The combinedthickness of the spacer 24 and sidewall is preferably controlled toensure that the space between the impurity diffused layers 20 and thedummy gate electrode 52 is filled.

As has been described, the dummy gate electrode 52 is formed surroundingthe impurity diffused layers 20 in the semiconductor device 400. Thiscan more effectively inhibit ions from penetrating through the partialisolation insulator 8 during implantation in the impurity diffusedlayers (extension and source/drain) 20. Accordingly, ion penetrationaround the impurity diffused layers 20 can also be inhibited anddegradation of isolation characteristics of the SOI layer 6 can beeffectively prevented.

While the fourth embodiment has been described with respect to a casewhere a dummy gate electrode 52 is formed around a semiconductor device100 similar to the one in the first embodiment, the present invention isnot so limited. For example, the dummy gate electrode 52 may be combinedwith any of the other semiconductor devices described in the first tothird embodiments.

FIG. 20 is a schematic diagram illustrating another exemplarysemiconductor device 410 according to the fourth embodiment. As shown inFIG. 20, a dummy gate electrode 152 is formed in the semiconductordevice 410. Unlike the dummy gate electrode 52 in the semiconductordevice 400, which is one integral element, the dummy gate electrode 152in the semiconductor device 410 has multiple small dummy gate electrodesegments arranged to occupy the region equivalent to the region occupiedby the dummy gate electrode 52. Each segment of the dummy gate electrode152 is sized to design rule minimum dimensions and the space between theadjacent dummy gate electrodes 152 is filled with a silicon oxide filmor silicon nitride film during sidewalls or the like are formed.

This arrangement also can reduce the resistance of the semiconductordevice. In addition, because the dummy gate electrode 152 is segmented,the flatness of an insulator subsequently formed to cover the gateelectrodes and other elements can be improved in CMP planarization.

FIG. 21 is a schematic diagram illustrating another exemplarysemiconductor device 420 according to the fourth embodiment of thepresent invention.

The semiconductor device 420 shown in FIG. 21 has the same structure asthat of the semiconductor device 400 shown in FIGS. 19A and 19B, exceptthat a complete isolation insulator 42 is provided on both sides of oneend 14 b of a gate electrode 14 as in the semiconductor device 200 shownin FIGS. 13A to 13C. That is, the SOI layer 6 on both sides of end 14 bof the gate electrode is etched down to the buried insulator 4 and theetched portion is filled with a silicon oxide film. As shown in FIG. 21,ends of the dummy electrode 52 overlap the both ends of the completeisolation insulator 42 in the semiconductor device 420. The provision ofthe complete isolation insulator 42 in the semiconductor device havingthe dummy gate electrode 52 can reduce the parasitic capacitance toimprove the device characteristics of the semiconductor.

Fifth Embodiment

FIGS. 22A to 24B are schematic diagrams illustrating process steps formanufacturing a semiconductor device according to a fifth embodiment ofthe present invention. FIGS. 22A, 23A and 24A and FIGS. 22B, 23B and 24Bshow portions corresponding to those in FIGS. 1A and 1B, respectively.

The semiconductor device 500 according to the fifth embodiment is thesame as the semiconductor device 100 shown in FIGS. 1A and 1B, exceptthat the shape of the gate electrode 60 is different.

In particular, the gate electrode 60 in the semiconductor device 500 islonger in the longitudinal direction than that of the semiconductordevice 100. However, the length in the Y-direction of the portion onboth sides of which an impurity diffused layers 20 are formed is thesame as that of the semiconductor device 100 and the length of the end60 b of the gate electrode 60 on both sides of which the impuritydiffused layers 20 are not formed is longer than that in thesemiconductor device 100.

The method for manufacturing the semiconductor device 500 shown in FIGS.22A and 22B is the same as the method for manufacturing thesemiconductor device 100 shown in FIG. 2, except that resist masks usedduring ion implantation at steps S32, S34, S38, and S40 vary in shape.In particular, a resist mask 62 which is formed on the body potentialfixing region 22 side before an extension of the impurity diffusedlayers 20 is formed (step S32) extends to cover a portion of the end 60b of the elongated gate electrode 60, as shown in FIG. 22. The end 60 bof the gate electrode 60 is longer than regular gate electrodes.Therefore, the region on the both side of the end 60 b of the gateelectrode 60 where the impurity diffused layers 20 is not provided doesnot cause a problem.

For ion implantation into the body potential fixing region 22 (stepS34), a resist mask 64 is formed so as to cover a portion of a dummygate 16 on the side opposite the gate electrode 60 as shown in FIGS. 23Aand 23B. The provision of the resist mask 64 in this way does not causea problem, because a partial isolation insulator 8 is formed under thedummy gate electrode 16 and the portion does not need ion implantation.Covering the portion of the dummy gate electrode 16 with the resist mask64 can inhibit ions implanted with ion implantation into the bodypotential fixing region 22 from penetrating through the partialisolation insulator 8 into the well to increase its resistance.

Similarly, after sidewalls are formed, as in FIGS. 24A and 24B, a resistmask 66 is provided in such a manner that it covers the portion of theend 60 b of the gate electrode 60 and ion implantation for thesource/drain in the impurity diffused layers 20 is performed. Then,before ion implantation into the body potential fixing region 22, aresist mask is formed in a manner similar to that shown in FIGS. 22A and22B.

As has been described above, there is a region always covered with aresist mask during ion implantation because the resist masks 62 and 66are extended to cover the end 60 b of the gate electrode 60. This regionis a portion of the surface of the partial isolation insulator 8 wherepenetration of ions must be inhibited. Therefore, by always covering theportion with a resist mask, ions can be inhibited from penetratingthrough the partial isolation insulator 8 into the SOI layer 6 duringion implantation. Thus, degradation of isolation characteristics of theSOI layer 6 can be prevented.

It should be noted that the tolerance of alignment of resist masks withthe gate electrode 60 is large because the length of the gate electrode60 is elongated. Therefore, a misalignment of resist mask 62 or 66 withthe gate electrode 60 can be inhibited to provide a semiconductor devicethe resistance of which is more reliably reduced.

While the fifth embodiment has been described with respect to an examplewith which a semiconductor device 100 of the first embodiment iscombined, the present invention is not so limited. For example, thefifth embodiment can be combined with any of other semiconductor devicesdescribed in the first to fourth embodiments to form overlapped resistmasks in process steps. This can inhibit ion penetration through thepartial isolation insulator 8 more reliably to reduce the resistance ofthe semiconductor device.

Sixth Embodiment

FIG. 25 is a top view illustrating a semiconductor device 600 accordingto a sixth embodiment of the present invention. For indicating electricconnections, only wirings, electrode, and a diffusion layer are shown.FIGS. 26 and 27 are cross-sectional views of the semiconductor device600, showing cross-sections taken on line X-X′ and line Y-Y′ of FIG. 25,respectively.

As shown in FIG. 25, the semiconductor device 600 is a semiconductordevice 100 described in the first embodiment to which wirings 70, 72,and 74 are attached.

Referring to FIGS. 26 and 27, in the semiconductor device 600, a partialisolation insulator 8 is formed on an SOI substrate consisting of aunderlying silicon substrate 2, a buried insulator 4, and an SOI layer6, and a gate electrode 14 is formed on a gate insulator 12, as in thefirst embodiment. Also formed on the partial isolation insulator 8 is adummy gate electrode 16. Impurity diffused layers 20 and a bodypotential fixing region 22 are formed in predetermined locations in theSOI layer 6. On the sides of the gate electrode 14 and dummy gateelectrode 16, a spacer 24, a silicon oxide film 26, and a siliconnitride film 28 are formed. This structure is the same as that describedwith respect to the first embodiment and the dummy gate electrode 16inhibits ions from penetrating through the partial isolation insulator 8into the layer immediately below it.

The surface of the gate electrode 14 and the dummy gate electrode 16 anda portion of the surface of the impurity diffused layers 20, and thesurface of the body potential fixing region 22 are silicided to formmetal silicide layers 80, 82, 84, and 86. An interlayer film 88 isformed over the SOI layer 6 to cover the gate electrode 14, the dummygate electrode 16, and other elements. Contacts 90 are formed in theinterlayer film 88. The contacts 90 connect the impurity diffused layers20 to aluminum wirings 70, the gate electrode 14 to an aluminum wiring72, and the body potential fixing region 22 to an aluminum wiring 74.

One example of the sixth embodiment has been described in which wiringsare provided on the upper layer of the semiconductor device 100.However, connections of wirings with the gate electrode 14 and theimpurity diffused layers 20 are not limited to this example but otherstructure may be used. These connections can be provided in any of othersemiconductor devices 200-500 of the second to fifth embodiments, ofcourse. That is, wirings and plugs are formed in appropriate locationsand are electrically connected to the gate electrodes, impurity diffusedlayers, and body potential fixing region in the semiconductor devices200-500 described with respect to the first to fifth embodiments.

It should be noted that the SOI substrate consisting of the underlyingsilicon substrate 2, buried insulator 4, and the SOI layer 6 in thefirst to sixth embodiments represents a “substrate” including an“underlying silicon substrate”, a “buried insulator”, and a“semiconductor layer” of the present invention, the gate electrode 14 or60 represents a “first gate electrode” of the present invention, thedummy gate electrode 16 or 116 represents a “second gate electrode” ofthe present invention, and the impurity diffused layers 20, the bodypotential fixing region 22, and the partial isolation insulator 8represent an “impurity diffused region”, a “second impurity diffusedregion”, and a “first insulator”, respectively, of the presentinvention. The complete isolation insulator 42 according to the secondembodiment, for example, represents a “complete isolation insulator” ofthe present invention and end 114 b of the gate electrode in thevariation of the second embodiment 2 represents a “portion formed on thecomplete isolation insulator”. The silicon oxide film 50 in the thirdembodiment, for example, represents a “second insulator” of the presentinvention and the dummy gate electrodes 52, 152 in the fourthembodiment, for example, represent a “third gate electrode” of thepresent invention.

Furthermore, a “first insulator forming step” is implemented byperforming steps S2 to S20, for example; a “first and second gateelectrode forming step” is implemented by performing steps S26 to S28; a“first resist mask forming step”, a “first impurity implanting step”,and a “first resist mask removing step” are implemented by performingstep S30 or S32; and a “second resist mask forming step”, a “secondimpurity implanting step”, and a “second resist mask removing step” areimplemented by performing step S32 or S34.

Seventh Embodiment

FIGS. 28A and 28B are schematic diagrams illustrating a semiconductordevice 700 according to a seventh embodiment of the present invention.FIG. 28A illustrates a top view of the semiconductor device 700 and FIG.28B illustrates a cross-section taken on line X-X′ in the portionenclosed in the ellipse “a” in FIG. 28A. The semiconductor device 700 inthe seventh embodiment will be described, which has multipletransistors, each including a gate electrode 714 a or 714 b and impuritydiffused layers 720 a or 720 b, and in which dummy gate electrodes 716are provided. For illustrating connections of elements such aselectrodes, only electrodes, wirings, and required impurity dopedregions are shown in FIG. 28A and the remaining elements are omittedfrom FIG. 28A. The thin solid lines in FIG. 28A represent impurity dopedregions formed on an SOI layer 706 and the thick solid lines representthe gate electrodes 714 a and 714 b, dummy gate electrodes 716, and awiring 770 formed in the metallization layer immediately above them. Thedotted lines represent wirings 772 formed in upper metallization layers.The semiconductor device 700 shown in FIGS. 28A and 28B is a cMOSFEThaving pMOSFETs and nMOSFETs formed on the SOI substrate.

In particular, the semiconductor device 700 has an SOI substrate havinga multilayered stack of a Si underlying substrate 702, a BOX layer(buried insulator) 704, and an SOI layer (semiconductor layer) 706, asshown in FIGS. 28A and 28B. The SOI substrate is isolated into activeareas in which nMOSs and pMOSs are to be formed by a complete isolationinsulator 710. The complete isolation insulator 710 is formed by etchingthe SOI layer 706 down to the BOX layer and filling the etched portionwith an oxide film. Gate electrodes 714 a and 714 b are formed on a gateinsulator 712 on active areas. Formed in each of the active areas aroundthe gate electrodes 714 a, 714 b is impurity diffused layers (extensionand source/drain) 720 a, 720 b (first impurity diffused region).

A well potential fixing region 722 (second impurity diffused region) isformed in the perimeter of the semiconductor device 700. The wellpotential fixing region 722 on the pMOS side is connected to a channelregion (body) under the gate electrode 714 a, 714 b through a well 718a, 718 b for fixing the potential of the body. Therefore, the wellpotential fixing region 722, as well as the body under the PMOS gateelectrode 714 a, 714 b, is implanted with n-type ions. The wellpotential fixing region 722 on the nMOS side is connected to a channelregion (body) under the gate electrode 714 a, 714 b through a well 718a, 718 b for fixing the potential of the body. Therefore, the wellpotential fixing region 722, as well as the body under the gateelectrode 714 a, 714 b of the nMOS, is implanted with p-type ions. Thewell 718 a, 718 b is formed by implanting ions into a thin portion ofthe SOI layer 706 which is etched down to a depth in the thickness ofthe SOI layer 706. A partial isolation insulator 708 is formed on thewell 718 a, 718 b at the same time when the complete isolation insulator710 is formed.

As has been stated with respect to the first to sixth embodiments, ifions penetrate into a portion (i.e. the well 718 a, 718 b) of the SOIlayer formed under the partial isolation insulator 708 during ionimplantation in the impurity diffused layers 720 a, 720 b or the wellpotential fixing region 722, the isolation characteristics of the wellcan degrade. Therefore, also in the semiconductor device 700, a dummygate electrode is provided in a PTI (Partial Trench Isolation) region inthe partial isolation insulator 708 under which the SOI layer 706 isformed, in order to prevent ion penetration.

However, forming a dummy gate electrode in every PTI region may prohibitreduction of size of the semiconductor device 700. The size of theimpurity diffused layers 720 a, 720 b of each transistor formed in thesemiconductor device 700 varies from transistor to transistor.Accordingly, the distance between the well potential fixing region 722and the impurity diffused layers 720 a, 720 b also varies fromtransistor to transistor. Accordingly, it can be difficult to form dummygate electrodes to fill the space between all gate electrodes 714 a, 714b and well potential fixing regions 722, because the space between agate electrode 714 a, 714 b and a well potential fixing region 722 canbe so small that a dummy gate electrode 716 cannot be formed inaccordance with a layout rule. In such a case, the whole semiconductordevice could be enlarged to provide space for forming dummy gateelectrode 716. However, this is not desirable because this does not meetthe demand for reduced semiconductor device size.

On the other hand, the impact of ion penetration during ion implantationis especially large for large (long) PTI regions. For small regions, anincrease in its resistance is relatively small. Therefore, especially ifthe PTI region is large, it is desirable that a dummy gate electrode 716be used to prevent ion penetration.

For this reason, a dummy gate electrode 716 is provided only in the PTIregion between agate electrode 714 b and a well potential fixing region722 where the distance between them is long. A dummy gate electrode isnot formed between a gate electrode 714 a and a well potential fixingregion 722 where the distance between them is short. With this, damageto connections by ion penetration can be inhibited without enlarging thewhole semiconductor device.

It should be noted that a dummy electrode 774 is formed in a region neara dummy gate electrode 716 on the partial isolation insulator 708 whereno electrode is formed nearby, thereby ensuring a uniform flatness insubsequent CMP.

FIG. 29 is a flowchart illustrating a method for manufacturing asemiconductor device 700 according to the seventh embodiment of thepresent invention. FIGS. 30 to 38 are schematic cross-sectional viewillustrating process steps for manufacturing the semiconductor device700 according to the seventh embodiment of present invention. FIGS. 30to 38 show cross-sections corresponding to the one shown in FIG. 28B.

First, a silicon oxide film 730, a polysilicon film 732, and a siliconnitride film 734 are formed in this order on top of an SOI substrateconsisting of Si underlying substrate 702, a box layer 704, and an SOIlayer 706 (steps S702 to 706), and a resist pattern 736 is formed on thesilicon nitride film 734 (step S708), as shown in FIG. 30. The resistpattern 736 is formed by photolithography in such a manner that anopening is provided in a region where a partial isolation insulator 708(or a complete isolation insulator 710) is to be provided.

Then, anisotropic etching is performed by using the resist pattern 736as a mask as shown in FIG. 31 (step S710). As a result, the siliconnitride 734, the polysilicon 732, and the silicon oxide 730 are etchedthrough and the SOI layer 706 is etched to some depth, thereby forming atrench in the SOI layer 706. Unnecessary resist pattern 736 is thenremoved (step S712).

Then, the inner wall of the trench is oxidized to form an oxide film 708a as shown in FIG. 32 (step S714). A resist pattern 738 is then formedin a region where a complete isolation insulator 710 is not to be formed(step S716). In particular, a resist pattern 738 is formed to coverregions where the SOI layer 706 is to be completely left for formingactive areas and a region (PTI) where some thickness of the SOI layer706 is left for forming a well 718 a, 718 b. The, the SOI layer 706 isetched together with the oxide film 708 a formed on the surface by usingthe resist pattern as a mask (step S718). Unnecessary resist patternS738 is then removed (step S720).

Then, a plasma silicon oxide 708 is formed as shown in FIG. 33 (stepS722) and CMP is performed (step S724). The CMP is stopped at thesurface of the silicon nitride 734. Then, an unnecessary portion of theplasma silicon oxide 708, and the silicon oxide 734 and the polysilicon732 are removed (steps S726 to S728).

Channel implantation is performed as shown in FIG. 34 (step S730). Thesemiconductor device 700 is a cMOS having n-type and p-type transistors.Therefore, when channel implantation for the pMOS regions is performed,a resist that covers the nMOS regions is formed and used as a mask toperform channel implantation. When channel implantation for the nMOSregions is performed, a resist that covers the pMOS regions is formedand used as a mask to perform channel implantation.

Then, a gate insulator 712 is formed as shown in FIG. 35 (step S732) anda gate polysilicon film 740 is formed (step S734). A resist pattern thatcovers regions where a gate electrode 714 a, 714 b, a dummy gateelectrode 716, and the dummy electrode 774 are to be formed is formed bya photoresist (step S736).

Then, the gate polysilicon 740 is etched by using the resist pattern 742as a mask, as shown in FIG. 36 (step S738). As a result, a gateelectrode 714 a, 714 b, a dummy gate electrode 716, and a dummyelectrode 774 are formed in appropriate locations. Unnecessary resistpattern 742 is then removed (step s740).

Then, spacers 724 are formed on the sides of the gate electrode 714 a,714 b, dummy gate electrode 716, and dummy electrode 774 as shown inFIG. 37 (step S742). The spacers 724 are formed by forming a siliconoxide film and then performing anisotropic etching. Then, pocketimplantation (step S744) and extension implantation (step S746) areperformed. For the pocket and extension implantations in the pMOSregion, a resist covering the nMOS region is formed and the resist, thegate electrode 714 a, 714 b, the dummy gate electrode 716, and the dummyelectrode 774 are used as a mask to perform implantation for forming apocket and then ion implantation for forming an extension. The resist isthen removed. For the pocket and extension implantations in the nMOSregion, on the other hand, a resist covering the pMOS region is formedand the resist, the gate electrode 714 a, 714 b, the dummy gateelectrode 716, and the dummy electrode 774 are used as a mask to performion implantation for forming a pocket and then ion implantation forforming an extension. Then the resist is removed. As a result, pocketsand extensions are formed around the gate electrode 714 a, 714 b. Itshould be noted that the dummy gate electrode 716 is formed on thepartial isolation insulator 708, which can prevent implanted ions frompenetrating through the partial isolation insulator and into the SOIlayer 706 below it.

Then, a sidewall 728 is formed on the sides of the gate electrode 714 a,714 b, the dummy gate electrode 716, and the dummy electrode 774 asshown in FIG. 38 (step S748). The sidewall 728 is formed by forming asilicon oxide film and a silicon nitride film and performing anisotropicetching.

Then, source/drain implantation is performed (step S750). For forming asource/drain in the pMOS region, a resist covering the nMOS region isformed and the resist, the gate electrode 714 a, 714 b, the dummy gateelectrode 716, and the dummy electrode 774 with the sidewalls 728 areused as a mask to perform ion implantation. For forming a source/drainin the nMOS region, on the other hand, a resist covering the pMOS regionis formed and the resist, the gate electrode 714 a, 714 b, the dummygate electrode 716, and the dummy electrode 774 with the sidewalls 728are used as a mask to perform ion implantation. In this way,sources/drains are formed in each nMOS and pMOS region. Afterunnecessary resists are removed, connections such as wirings are formedin layers as required to complete the semiconductor 700 shown in FIGS.28A and 28B.

It should be noted that the wiring pattern described with respect to theseventh embodiment does not limit the present invention. Any of otherwiring patterns may be used in which a PTI region where a dummy gateelectrode 716 can be formed is chosen and the dummy gate electrode 716is appropriately located in accordance with a wiring layout rule andrule minimum dimensions. Also, any of the configurations of thetransistors described with respect to the first to sixth embodiments maybe used for the layout of the dummy gate electrodes 716 described withrespect to the seventh embodiment.

The SOI layer 706 according to the present invention described above hasthe complete isolation insulator 710 formed by etching through the SOIlayer 706 except the regions for forming the active areas, wellpotential fixing region 722, and a well. However, the present inventionis not limited to structures in which such a complete isolationinsulator 710 is formed. For example, a structure may be used in which athin SOI layer 706 is left under the entire partial isolation insulator708, as in the first embodiment. To create such a semiconductor device,as shown in FIG. 39, a plasma silicon oxide 708 b may be formed (stepS722 in FIG. 29) immediately after the oxide film 708 a is formed atstep S714, without performing steps S716 to S720, and then CMP may beperformed (step S724) so that a part of the SOI layer 706 is left underthe entire partial isolation insulator 708.

Eighth Embodiment

FIGS. 40A and 40B are schematic diagram illustrating a semiconductordevice according to an eight embodiment of the present invention. FIG.40A illustrates the top view of the semiconductor device and FIG. 40Billustrates a cross-sectional view taken on line X-X′ of FIG. 40A. FIG.40A schematically illustrates a portion enclosed in ellipse “a” in FIG.28A.

The semiconductor device 800 shown in FIGS. 40A and 40B, is the same asthe semiconductor device 700 in FIGS. 28A and 28B, except that it hasdummy electrodes 874 (fourth gate electrodes) on both sides of a dummygate electrode 716, in place of the dummy electrodes 774, and furtherhas active dummies 876 (third impurity diffused regions) in the SOIlayer 706 under the dummy electrodes 874. Although, in FIGS. 40A and40B, for simplification, dummy electrodes 874 and active dummies 876 areillustrated only on the right side of the dummy electrode 716, dummyelectrodes 874 and active dummies 876 are provided on the left side ofdummy electrode 716 in actuality.

In particular, the active dummies 876 are arranged in a dot pattern ofSOIs and partial isolation insulators in the SOI layer 706, formed byproviding complete isolation insulators 810 in a regular array in theSOI layer 706.

The dummy electrode 874, on the other hand, is arranged in a dot patternformed on the active dummies 876 in the layer in which the dummy gateelectrodes 716 are formed. The active dummies 876 and the dummyelectrodes 874 are not completely coincide with each other viewed fromabove but are staggered in a given direction. That is, one dummyelectrode 874 overlaps different active dummies 876 near its fourcorners. It should be noted that the active dummies 876 are spaced apartfrom the SOI layer 706 in the PTI regions under the dummy gateelectrodes 716 and no active dummy 876 is formed in the PTI regionsunder the dummy gate electrodes 716.

As has been described above, in the semiconductor device 800 shown inFIGS. 40A and 40B, a dummy electrode 874 and active dummies 876 areprovided in spaces on both sides of a dummy gate electrode 716. Thus, alarge, flat space is filled with gate electrodes and therefore theflatness in CMP can be ensured. However, if there is sufficient spacefor forming dummy electrodes 874 and active dummies 876 only on one sideof dummy electrode 716, dummy electrodes 874 and active dummies 876 maybe formed only in the side.

Ninth Embodiment

FIG. 41 is a schematic diagram illustrating a semiconductor deviceaccording to a ninth embodiment of the present invention. FIG. 41illustrates only the dummy electrodes and its vicinity in thesemiconductor device 700 in FIG. 28A. The semiconductor device 900according to the ninth embodiment is the same as the semiconductordevice 700 in FIGS. 28A and 28B, except that the dummy gate electrodeshave a different structure.

As shown in FIG. 41, dummy gate electrodes 916 are formed at a locationequivalent to that of the dummy gate electrodes 716. In particular, inthe semiconductor device 900 in FIG. 41, a dummy electrode 916 is formedin a PTI region among the PTI regions between a well potential fixingregion 722 and impurity diffused layers 720, where there is sufficientspace for forming a dummy gate electrode. That is, in the semiconductordevice in which multiple transistors are formed as with the seventhembodiment, a dummy gate electrode 916 is selectively formed only in aspace between impurity diffused layers 720 and a well potential fixingregion 722 that is large enough for forming the dummy gate electrode.

Each of the dummy gate electrodes 916 is a set of dots 916 a, ratherthan a single large plane pattern. Each of the dots 916 a making up thedummy gate electrode 916 is sized and the dots are evenly spaced, inaccordance with a layout rule. The space between adjacent dots 916 a isfilled with sidewalls 928. That is, the space between dots 916 a isdetermined in accordance with a layout rule in such a manner that thespace is filled with the sidewall 928 formed.

FIGS. 42 to 44 are schematic diagrams illustrating process steps formanufacturing the semiconductor device 900 according to the ninthembodiment of the present invention. FIGS. 42 to 44 show a cross-sectionof a portion corresponding to the portion enclosed in ellipse “a” inFIG. 28A. The method for manufacturing the semiconductor device 900according to the ninth embodiment is similar to the process describedwith respect to the flowchart of FIG. 29.

However, as shown in FIG. 42, the resist pattern 942 formed at step S736in FIG. 29 for etching a gate polysilicon 940 is a dot resist pattern942 in which each dot corresponds to the position where each dot 916 aof a dummy gate electrode 916 is formed.

Then, the gate polysilicon 940 is etched in the shape of the dots 916 aof the dummy gate electrode 916 at step S738 and then the resist pattern942 is removed. Then, a spacer 924 is formed on the side of each dot 916a and the sides of the gate electrode 714 and the dummy electrode 774,as shown in FIG. 43. Then, after ion implantation is performed,sidewalls 928 are formed on the side of each of the dots 916 a and thesides of the gate electrode 714 and the dummy gate electrode 774 asshown in FIG. 44. As a result, the space between the dots 916 a isfilled with the spacer 924 and sidewall 928.

By forming the dummy gate electrode 916 as a set of dots 916 a, theflatness of an insulator in a subsequent CMP process can be improved. Inaddition, the space between the dots 916 a of the dummy gate electrode916 is designed in such a manner that the space is filled with thespacer 924 and sidewall 928. Therefore, during ion implantation in thesource/drain and the well potential fixing region 722, ions can beprevented from penetrating through the partial isolation insulator 708and into the SOI layer 706 under the partial isolation insulator 708.

The ninth embodiment has been described with respect to thesemiconductor device 900 with a structure in which a complete isolationinsulator 710 is formed in the SOI layer 706 and a PTI region isprovided with a portion of the SOI layer left only in a position wherethe body and the well potential fixing region 722 are to beinterconnected. However, the present invention is not so limited but astructure in which the complete isolation insulator 710 is not formedmay be used.

The shape of the dummy gate electrode 916 according to the ninthembodiment can be applied to the eighth embodiment. That is, the dummygate electrode 716 in the semiconductor device 800 of the eighthembodiment may be formed in a pattern like the pattern of dots 916 aaccording to the ninth embodiment. In that case, the dimensions andpitch of the dots 916 a of the dummy gate electrode 916 may be differentfrom the dimensions and pitch of the dot pattern of the active dummy 876and dummy electrode 874.

The number of arrays of dots 916 a and the shape of each dot 916 a shownin FIG. 41 do not limit the present invention. Furthermore, the patternof dots 916 a is not limited to a pattern in which dots 916 a are evenlyarranged in the region where the dummy gate electrode 916 is formed.

Tenth Embodiment

FIGS. 45 to 47 are schematic diagrams illustrating a semiconductordevice according to a tenth embodiment of the present invention. FIG. 45illustrates a top view of the semiconductor device, FIG. 46 illustratesa cross-section taken on line X-X′ of FIG. 45, and FIG. 47 illustrates across-section taken on line Y-Y′ of FIG. 45. The semiconductor device1000 shown in FIGS. 45 to 47 is the same as the semiconductor device 700shown in FIGS. 28A and 28B, except the pattern of dummy gate electrodes1016. FIGS. 45 to 47 show a layout in which a dummy gate electrode isformed between a gate electrode 714 b and a well potential fixing region722, as shown in the left-hand part of FIGS. 28A and 28B.

In particular, the dummy gate electrode 1016 surround each end of thegate electrode 714 b as shown in FIGS. 45 to 47. The space between thedummy gate electrode 1016 and the gate electrode is filled with a spacer1024 and a sidewall 1028. Referring to FIG. 47, the dummy gate electrode1016 partially overlaps the well potential fixing region 722. On theother hand, the edges of the dummy gate electrode 1016 does not overlapthe impurity diffused layers 720 b. This prevents occurrence of a leakcurrent.

The dummy electrode 1016 thus arranged is provided in place of the dummygate electrode 716 in FIGS. 28A and 28B. However, the present inventionis not so limited. A dummy electrode 1016 of this shape can be providedin such a manner that it surrounds the ends of all or some of the gateelectrodes 714 in the remaining part of the semiconductor device.

While the space between the dummy gate electrode 1016 and the gateelectrode 714 b is filled with a sidewall 1028 in the example describedwith respect to FIGS. 45 to 47, the present invention is not so limited.Depending on layout rules and the like, the space between a dummy gateelectrode 1016 and a gate electrode 714 b cannot be filled with asidewall 1028 alone. FIGS. 48A to 51B are schematic diagramsillustrating an example of the case. each of FIGS. 48A, 49A, 50A and 51Aillustrates a portion corresponding to the X-X′ cross-section in FIG. 45and each of FIGS. 48B, 49B, 50B and 51B illustrates a portioncorresponding to the Y-Y′ cross-section.

If the space between a dummy gate electrode 1016 and a gate electrode714 b is too large to be filled with a sidewall 1028 alone, anadditional, oxide sidewall 1030 is formed to fill the space between thegate electrode 714 b and the dummy gate electrode 1016.

In particular, after sidewalls are formed in step S748 as shown in FIGS.48A and 48B, a plasma silicon oxide film 1030 a is formed over them asshown in FIGS. 49A and 49B. The thickness of the plasma silicon oxidefilm 1030 a is chosen to be at least half the distance between sidewalls1028. Then, etch-back is performed by using anisotropic dry etching toform oxide sidewalls 1030 (third insulator) as shown in FIGS. 50A and50B. Isotropic etching is then performed to remove unnecessary siliconoxide film 1030 a, as shown in FIGS. 51A and 51B. Here, the etching isperformed by setting conditions such that the silicon oxide film 1030 aon the impurity diffused layers 720 a, 720 b and on the well potentialfixing region 722 is removed and the oxide sidewall 1030 between thedummy gate electrode 1016 and the gate electrode 714 is left. As aresult, the space between the gate electrode and the dummy gateelectrode is filled with the oxide sidewall.

It should be noted that the method of filling the space with an oxidesidewall 1030 after a sidewall is formed can be applied to any of thefirst to ninth embodiments if, for example, the space between dotpatterns 916 a constituting a dummy gate electrode 916 cannot be filledwith a single sidewall alone in the ninth embodiment.

The features and the advantages of the present invention as describedabove may be summarized as follows.

According to one aspect of the present invention, in the semiconductordevice, on a first isolator between a first gate electrode and a secondimpurity diffused region, a second gate electrode is formed. The secondgate is used as a mask during ion implantation for forming a firstimpurity diffused region. This can prevent ions from penetrating throughthe first insulator and into a semiconductor layer under the firstisolator. Consequently, degradation of isolation characteristics can beinhibited and the yields of production of semiconductor devices can beincreased.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay by practiced otherwise than as specifically described.

The entire disclosures of a Japanese Patent Application No. 2005-35985,filed on Feb. 14, 2005 and No. 2005-372223, filed on Dec. 26, 2005including specifications, claims, drawings and summaries, on which theConvention priorities of the present application are based, areincorporated herein by references in its entirety.

1. A semiconductor device comprising: a substrate including anunderlying silicon substrate, a buried insulator, and a semiconductorlayer; a first gate electrode formed on a gate insulator on thesemiconductor layer; a first impurity diffused region formed in a regionaround the first gate electrode in the direction of the length of thefirst gate electrode in the semiconductor layer by implanting with animpurity of a first conductivity type; a second impurity diffused regionformed in a region in the semiconductor layer in the direction of anextension line of the length of the first gate electrode by implantingwith an impurity of a second conductivity type opposite the firstconductivity type; a first insulator which is formed at least on aregion of the semiconductor layer between the second impurity diffusedregion and the first gate electrode; and a second gate electrode formedon the first insulator between the second impurity diffused region andthe first gate electrode, wherein the first insulator has a completeisolation region on both sides of the width of the first gate electrodeat an end of the first gate electrode opposed to the second gateelectrode, the complete isolation region penetrating through thesemiconductor layer down to the buried insulator.
 2. A semiconductordevice comprising: a substrate including an underlying siliconsubstrate, a buried insulator, and a semiconductor layer; a first gateelectrode formed on a gate insulator on the semiconductor layer; a firstimpurity diffused region formed in a region around the first gateelectrode in the direction of the length of the first gate electrode inthe semiconductor layer by implanting with an impurity of a firstconductivity type; a second impurity diffused region formed in a regionin the semiconductor layer in the direction of an extension line of thelength of the first gate electrode by implanting with an impurity of asecond conductivity type opposite the first conductivity type; a firstinsulator which is formed at least on a region of the semiconductorlayer between the second impurity diffused region and the first gatee1ectrode; and a second gate electrode formed on the first insulatorbetween the second impurity diffused region and the first gateelectrode, wherein the first insulator is also formed in a regionsurrounding the first impurity diffused region, and the semiconductordevice further comprises a third gate electrode formed on the firstinsulator in such a manner that the third gate electrode surrounds thefirst impurity diffused region.
 3. The semiconductor device according toclaim 2, wherein the third gate electrode consists of a plurality ofsegments of electrode surrounding the first impurity diffused region. 4.A semiconductor device comprising: a substrate including an underlyingsilicon substrate, a buried insulator, and a semiconductor layer; afirst gate electrode formed on a gate insulator on the semiconductorlayer; a first impurity diffused region formed in a region around thefirst gate electrode in the direction of the length of the first gateelectrode in the semiconductor layer by implanting with an impurity of afirst conductivity type; a second impurity diffused region formed in aregion in the semiconductor layer in the direction of an extension lineof the length of the first gate electrode by implanting with an impurityof a second conductivity type opposite the first conductivity type; afirst insulator which is formed at least on a region of thesemiconductor layer between the second impurity diffused region and thefirst gate electrode; and a second gate electrode formed on the firstinsulator between the second impurity diffused region and the first gateelectrode, wherein the second gate electrode is divided into a pluralityof segments which are arranged at predetermined intervals.
 5. Thesemiconductor device according to claim 4, wherein the space between thesegments of the second gate electrode arranged at the predeterminedintervals is filled with a sidewall.
 6. The semiconductor deviceaccording to claim 5, wherein the space between the second gateelectrode and the first gate electrode is further filled with a thirdinsulator.
 7. A semiconductor device comprising: a substrate includingan underlying silicon substrate, a buried insulator, and a semiconductorlayer; a first gate electrode formed on a gate insulator on thesemiconductor layer; a first impurity diffused region formed in a regionaround the first gate electrode in the direction of the length of thefirst gate electrode in the semiconductor layer by implanting with animpurity of a first conductivity type; a second impurity diffused regionformed in a region in the semiconductor layer in the direction of anextension line of the length of the first gate electrode by implantingwith an impurity of a second conductivity type opposite the firstconductivity type; a first insulator which is formed at least on aregion of the semiconductor layer between the second impurity diffusedregion and the first gate electrode; and a second gate electrode formedon the first insulator between the second impurity diffused region andthe first gate electrode, a plurality of third impurity diffused regionsformed in the semiconductor layer on a side of the second gate electrodeat predetermined pitches and at predetermined intervals; and third gateelectrodes formed on the plurality of third impurity diffused regions atpredetermined intervals.
 8. A method for manufacturing a semiconductordevice, comprising the steps of: forming a first insulator whichseparates a semiconductor layer of a silicon-on-insulator substrateincluding an underlying substrate, a buried insulator formed on top ofthe underlying substrate and a semiconductor layer formed on top of theburied insulator, into first and second regions; forming a gateinsulator on the semiconductor layer; forming a first gate electrode onthe first region and a second gate electrode on the first insulator;forming a first resist mask covering the second region; implanting animpurity of a first conductivity type into the first region by using thefirst resist mask and the first and second gate electrodes as a mask;removing the first resist mask; forming a second resist mask coveringthe first region; implanting a second impurity of a second conductivitytype into the semiconductor layer by using the second resist mask; andremoving the second resist mask.
 9. The method for manufacturing asemiconductor device according to claim 8, wherein the first resist maskis formed in such a manner that the first resist mask covers at least aportion of the second gate electrode.
 10. The method for manufacturing asemiconductor device according to claim 8, wherein the second resistmask is formed in such a manner that the second resist mask covers atleast a portion of the first gate electrode.